The present invention relates to a device for dispersing a liquid in a gas phase, particularly by spraying the liquid, which is confined in a bed or tank, upwardly to disperse it in the gas phase.
A particularly important field in which devices of this kind are used is in the aerators of waste-water treatment installations, which utilise a biological reaction for purification of activated sludge.
In this technique of purifying waste-water, various types of aerating devices have successively been developed.
For example, overpressure systems are known, which are adapted to supply air to a pipe located near the floor level of the activating tank, this pipe being perforated or equipped with porous diffusers, in order to promote the formation of air bubbles which move upwards through the mass of fluid to be aerated.
Another technique uses horizontal rotary brushes, the axis of which are located above the water level, so that radial elements, either flexible in the form of bristles, or rigid in the form of blades, beat the water like paddle wheels.
Finally, surface turbines have been developed, which are provided with a vertical rotor equipped with a body submerged at water level, this body beating the air-water interface so as to project a water spray into the air.
The invention is developed from the state of the art represented by the third category of appliances, comprising a pump, which is at least partly submerged in the liquid between a flared suction tube and a delivery nozzle. Experience shows that in appliances of this kind, the screw constituting the active member of the pump has a relatively poor output, which is attributable to the necessarily limited height of the water spray, this height generally being distinctly less than, for example, one meter.
As is known, in order to ensure good aeration, it is sufficient to produce a spray which disperses the drops in a shower of very small height (less than one meter, as mentioned above); in fact, the liquid-air interface is saturated almost immediately.
Conversely, at total heads of water as low as this, the output of hydraulic pumps is very poor. Moreover, these surface aerators offer no possibility of a rational solution to the problem of mixing the lower layers of liquid (near to the floor of the tank) with the intermediate and surface layers; to obtain such a mixture, even imperfectly, it is necessary, with the devices known hitherto, to expend agitating power which is superfluous in relation to the oxygen requirement.
Specific prior art devices include the delivery nozzle described in French Pat. No. 2,195,476 (Harivel) which nozzle is located near the liquid-gas interface and which has an outer surface provided with a widened profile, and the disclosure of French Pat. No. 2,023,739 (Sydnor Hydro-Dynamics) which describes a driving motor arranged beneath the pump.
The object of the invention is to provide a device of the kind referred to which offers a considerably improved energy efficiency in comparison with known surface turbines.
Another object of the invention is to produce an aerator adapted to provide conditions which are particularly favourable to the effectiveness of biological processes for treating waste-water.